"Method Not Found" error in OS Integration project: works in VS, doesn't in OS.

So everything was working fine before. Unfortunately, I am not sure what I might have changed.
So, I have an integration and whenever I call a particular method, it says this:

"Method not found: 'BreezeWeb.Unipay.UnipayResponse`1<BreezeWeb.Unipay.Processing.Models.Sale> BreezeWeb.Unipay.Processing.API.Sale(Int32, BreezeWeb.Unipay.Enums.AccountType, System.String, System.String, System.String, System.String, Int32, System.String, System.String, System.String, System.String)'."

That "Sale" method is from an external DLL. When I add a UnitTest project to the solution for the XIF and debug a quick test, everything works just fine and the method runs. I compile and push to OutSystems, and I get that error. Is there possibly something out of sync when pushed to OutSystems?

I'm really confused right now and not even sure what I would need to provide to get help for troubleshooting, besides that error message.

Can you create an sample that maybe has a simple form and your extension? Is that external DLL bundled into the integration? Ie.. in visual studio change the property of the external dll so it compiles into it instead of staying external